For the past couple of days I've been having problems uploading things. I went to speedtest.com yesterday and download speed was normal but when it tried to do the upload speed test it just sat on "connecting" and didn't even complete it. I can sometimes upload things, sometimes not, and it's very slow. For instance, when I try to upload a photo on my phone to Instagram, on out wireless network it sits there forever then fails. But on 3G it uploads very quickly. Does this sound like a problem with my networking equipment, or something on Comcast's end? Any input would be appreciated.

Comcast probably. I would connect your computer strait to the modem, pwr cycle your modem, make sure all the cables are tight, and if it still does it call comcast (because they are going to tell you to do the same thing likely, lol). Sounds like an snr issue.

I had the same issue. The problem symptom disappeared if the router was bypassed. But that does not necessarily mean that the culprit is the router. My experiments for troubleshooting indicated that the facility at Comcast's side BECAME incompatible with my router. Comcast did not admit this so I temporarily switched the router with a backup router of a different brand. Then periodically I tried back the original router to see when Comcast would restore the original state. I had to wait a couple of months before I restored the original router.

C: Go to your modem's management page (mine's 192.168.100.1 but that's by no means universal) and click on whatever you need to find the various signal levels. The upstream power level should be below 50 dBmV. If it's close to 60, either your modem is shot or you've got a bad connection to the head-end (usually too many splitters in the way).

Never ask a woman who is eating ice cream straight from the carton how she's doing.

Please note that I presently do not have any upload speed problem. I merely stated my experience with Comcat ISP service because the OP appears to be having the same problem.BTW: Checking the upstream power level was one of the trouble shooting steps and was found unchanged since I started using the modem, and that was 39.75dBmV. As the OP stated, to measure the upload(& download) speed, I use speedtest.net while any other traffic to and from the Internet stopped.

C: Go to your modem's management page (mine's 192.168.100.1 but that's by no means universal) and click on whatever you need to find the various signal levels. The upstream power level should be below 50 dBmV. If it's close to 60, either your modem is shot or you've got a bad connection to the head-end (usually too many splitters in the way).

Actually http://192.168.100.1/ -is- universal. it works literally with every known cable modem in existence.

Solution: I got a replacement for my old router (Belkin N750DB wireless dual band N+), and now everything works. Still puzzled why that works, but thanks everybody for voicing in. It gave me some good data when working with Comcast.

We received UPnP responses from one device:192.168.0.1: this device provided a valid device description via its UPnP URL. This description, viewable here, contains the following information about this gateway:Manufacturer: D-LinkModel name: D-Link RouterModel number: DIR-655